<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <style>
            body {
                font-size: 60px;
            }

            .box1 {
                width: 200px;
                height: 200px;
                background-color: #bfa;
                position: absolute;

                /* 
                    对于开启了定位元素,可以通过z-index属性来指定元素的层级
                        z-index需要一个整数作为参数,值越大元素的层级越高
                            元素的层级越高越优先显示
                        
                        如果元素的层级一样,则优先显示靠下的元素
                */
                z-index: 1;
            }

            .box2 {
                width: 200px;
                height: 200px;
                background-color: rgba(255, 0, 0, .3);
                
                position: absolute;
                top: 100px;
                left: 100px;
            }

            .box3 {
                width: 200px;
                height: 200px;
                background-color: yellow;
                position: absolute;
                
                top: 200px;
                left: 200px;


            }
        </style>
    </head>
    <body>
        <div class="box1">1</div>
        <div class="box2">2</div>
        <div class="box3">3</div>
    </body>
</html>